1. Field of the Invention
This invention relates to an air conditioning system and, more particularly, it relates to a system adapted to circulate a fluid which can change a phase between a gas phase and a liquid phase through a heat source side unit and a plurality of user side units more than half of which are disposed below the heat source side unit in terms of number by utilizing the difference in specific gravity between the liquid phase and the gas phase of the fluid and the discharging force of a pump arranged along a liquid phase pipe so as to make each of the user side units at least capable of cooling ambient air.
2. Background Art
FIG. 13 of the accompanying drawings schematically illustrates a known air conditioning system of the type under consideration disclosed in Japanese Patent Application Laid-Open No. 7-151359. Referring to FIG. 13, it comprises components including an exterior heat exchanger (hereinafter referred to as heat source side unit) 1 adapted to supply cold or hot water, a plurality of user side units 4 disposed at a level lower than that of the heat source side unit 1, each having a heat exchanger 5 and a flow control valves 8, a motor pump 10 and a number of switch valves 11 through 14, which components are connected by way of liquid phase piping 6 and gas phase piping 7 to form a closed circuit 3 so that a refrigerant sealed in the closed circuit 3 circulates through the heat source side unit 1 and the user side units 4 to provide the user side units 4 with a cooling/heating effect. Reference symbol S14 denotes a liquid level sensor arranged at the user side unit 1 for controlling the motor pump 10 so as to provide the user side unit 1 constantly with a given amount of refrigerant when the system is in operation.
With the known air conditioning system having a configuration as described above, assume here that the temperature of the room where one of the user side units 4 is installed is raised. If the switch valves 11 and 12 are closed whereas the switch valves 13 and 14 are opened along with the flow control valve 8 to feed the user side unit 1 with cooling water for cooling and condensing the refrigerant while the motor pump 10 is at rest, then the refrigerant condensed in the user side unit 1 falls through the liquid phase piping 6 by its own weight to flow into the heat exchanger 5 of the user side unit 4 by way of the switch valves 13 and 14 and the related flow control valve 8.
The refrigerant flown into the heat exchanger 5 absorbs heat from the air in the room by way of the pipe walls of the heat exchanger to cool the inside of the room to become evaporated and flow into the gas phase piping 7 and then to the heat source side unit 1 where the refrigerant is condensed to reduce the internal pressure so that a natural circulation is established in the system without driving the motor pump 10 to forcibly circulate the refrigerant even in summer when the power consumption level may be maximal in the local community. Thus, such a system provides a great advantage of reducing the running cost particularly when the system is in full operation.
If, on the other hand, the switch valves 11 and 14 are closed whereas the switch valves 12 and 13 are opened along with the flow control valve 8 and the motor pump 10 is driven to cool and condense the refrigerant sealed in the closed circuit 3 by the cooling effect of the heat source side unit 1, then the condensed refrigerant in the heat source side unit 1 flows down through the liquid phase piping 6 by its own weight and the discharging effect of the motor pump 10 to get into the heat exchanger 5 by way of the flow control valve 8 so that a circulation of refrigerant is forcibly established to provide a cooling effect in the room.
Thus, when the motor pump lo is driven for cooling, the system provides an advantage of supplying the heat exchanger 5 of the user side unit 4 with refrigerant at an sufficiently high rate, if the unit 4 is arranged on an upper floor located directly below the heat source side 1.
Now, assume that the temperature of the room where one of the user side units 4 is installed falls. If the switch valves 13 and 14 are closed whereas the switch valve 11 and 14 are opened along with the flow control valve 8 and the motor pump 10 is driven to supply the heat source side unit 1 with hot water and heat and evaporate the refrigerant sealed in the closed circuit 3, then the vapor of refrigerant produced in the heat source side unit 1 is made to flow into the heat exchanger 5 by way of the gas phase piping 7.
The vapor of refrigerant flown into the heat exchanger 5 emits heat into the room by way of the pipe walls of the heat exchanger 5 to raise the temperature in the room and, at the same time, become condensed before it flows into the liquid phase piping 6 and then back to the heat source side unit 1 by way of the switch valves 14 and 11 under the driving effect of the motor pump 10 to establish a circulation of refrigerant so that the user side unit 4 keeps on operating to heat the inside of the room.
With the above described known air conditioning system according to Japanese Patent Application Laid-Open No. 7-151359, while the power consumption rate and hence the running cost of the system are reduced in summer when the power consumption level may be maximal in the local community if the motor pump is held at rest to establish a natural circulation of refrigerant, the user side units may not operate effectively for cooling nor provide a satisfactory cooling effect when they are arranged at a level close to that of the heat source side unit.
If the motor pump is driven for cooling, the power consumption rate of the motor pump will become significant although the user side units that are arranged at a level close to that of the heat source side unit may be fed with refrigerant at a sufficient rate to provide a satisfactory cooling effect. It will be appreciated that the power consumption rate of the motor pump will always be significant because the motor pump has to have a large output power that can draw the refrigerant condensed in the user side units up to the heat source side unit located higher than them.
Thus, there is a need for a air conditioning system that can provide a satisfactory cooling effect and, at the same time, effectively suppress the power consumption rate even in mid summer when the power consumption level may be maximal in the local community.
Additionally, known air conditioning systems of the type under consideration are accompanied by a drawback of unsatisfactory operation that appears when the pressure of the refrigerant contained in the closed circuit drops abruptly while the system is operating for cooling because the refrigerant in the liquid phase piping starts boiling to produce bubbles and becomes unable to play its role. Another drawback of known air conditioning systems is that most of the refrigerant in the liquid state can held in the heat source side unit when the system is operating for cooling so that only an insufficient amount of refrigerant circulates through the user side units.